HEC-RAS performs lots of maths on this data and generates water levels for the stream. These water levels are used for many purposes, such as flood insurance, emergency planning, and municipal codes on new construction.

HEC-RAS is a GUI replacement for HEC-2, with many new features and updated formulae. HEC-RAS version 3.0.1 was released in April 2001. Haestad Methods, Inc. distributes and supports this software.